This invention relates to a tape cassette, for example, a videocassette of the VHS format, equipped with reel detents to keep tape reels inside from idly turning when the cassette is inoperative.
The housing of a conventional tape cassette such as of video tapes contains a pair of tape reels around which a length of tape is wound, and is provided with reel detents adapted to mesh with toothed peripheries of the tape reels to keep the reels from turning when not in use. The reel detents are swingably supported by pivots formed upright on the inner wall of one of two halves of the housing. When the cassette is used, a release pin of a tape recorder-reproducer (hereinafter called a tape recorder or recorder) turns the reel detents off from the braking position.
FIGS. 5 and 6 illustrate a typical arrangement of reel detents and neighboring parts in a conventional VHS videocassette. Numeral 1 designates the lower half of a cassette housing; 2, a pair of tape reels; 3, pivots for reel detents; and 4, reel detents. The peripheries of the tape reels 2 are formed with tooth-like indentations. When the cassette is not in use, pawls at the upper ends of the reel detents 4 are in mesh with the indentations to check the motion of the reels. As the cassette is pushed into a tape recorder, a release pin 6 of the recorder comes in to press a release lever 5 and turn it in the direction of the arrow. The release lever thus pushes legs 7 of the reel detents 4, causing the detents 4 to turn about the pivots and liberate the tape reels 2.
FIGS. 3 and 4 show the reel detents set free in unengaged position, FIG. 4 being a cross-sectional view taken along line 4--4 of FIG. 3. Each of the pivots 3 for the reel detents is in one piece with the lower housing half 1, formed together by molding, and upright on the bottom wall of the housing half 1.
The pivots for reel detents are required to have a sufficient diameter to maintain the strength for proper functioning. Actually, in the fabrication of cassette housings, the mold construction usually renders it difficult to efficiently expose the reel detent pivots to cooling water for solidification, making the pivots the last portions to be cooled in the molding process. Although one approach to the reduction of manufacturing cost might be "cycle speedup" (shortening of the molding cycle per piece), the approach is being questioned because it would entail deformation of the detent pivots that cool so slowly. Past endeavors to shorten the molding cycle under the existing conditions led to tilting or deformation of the pivots, thus presenting a productivity problem.
Japanese Utility Model Application Kokai No. 4-47811 proposes an attempt to speed up the cycle. It contemplates reducing the overall thickness or volume of reel detent pivots while securing the necessary diameter, and thereby increasing the cooling rate of the pivots. To be more exact, as shown in FIG. 7, an upright column of a given diameter is formed with a plurality of axially extending recesses at equal intervals circumferentially. Thus a pivot 3 of a configuration such that a plurality of ribs 8 having a predetermined thickness T are equidistantly formed radially. This construction allows the pivot to cool rapidly on molding and accordingly speeds up the cycle of molding a cassette housing.
It is true that a pivot having radial ribs as taught in Utility Model Application Kokai 4-47811 cools rapidly upon molding. However, because the portions inside the mold that form the ribs provide narrow and complex passages for molten resin, the resin flow tends to become uneven. This results in variations of rib thickness and failure to give a truly round outside diameter of the pivot. Moreover, many sharp corners formed along the outermost diametral portion of the pivot easily produce burrs, which can increase friction with the reel detent in engagement and affect its performance adversely. Further, the limited mold cavity to form the radial ribs interrupts smooth flow of molten resin, and calls for a high enough molding pressure to ensure the smooth flow at an economic disadvantage.
Therefore, the present invention aims at obtaining a tape cassette having detent lever pivots which can be solidified upon molding at the same rate as the other housing portions even when the molding cycle is cut down, with uniform resin flow ensured, the pivots as molded having fewer burrs than usual, good roundness, and sound balance.